This is an invention in lighting. More particularly, it involves an arrangement for conserving power in the operation of fluorescent lamp systems.
This application is related to U.S. patent application Ser. No. 629,868, filed Dec. 19, 1990 and U.S. patent application Ser. No. 673,692 filed, Mar. 21, 1991 both of which are assigned to the same assignee as this application. Both of these applications are hereby incorporated by reference herein.
It is desirable to decrease the power expended by fluorescent lamps by shutting off the current to the heater electrodes of such lamps after ignition. In the past a number of arrangements for doing this have been proposed. Some of these use relays (see U.S. Pat. No. 4,661,745 to Citino et al and U.S. Pat. No. 4,954,749 to Crawford). Relays can be noisy and are subject to wear. The use of a filament transformer has also been proposed (see U.S. Pat. No. 4,399,391 to Hammer et al). Arrangements with filament transformers require auxiliary protection against excessive currents which can be developed in case a lamp electrode is damaged and the lamp acts in the manner of a rectifier.